The present invention relates to electronics and, more particularly, to analog ping techniques for wireless charging and powering of wireless receivers.
Wireless energy transfer or wireless power is the transmission of electrical energy from a power source to an electrical load without interconnecting wires. Such wireless charging is useful in cases where interconnecting wires are inconvenient, hazardous, or costly. Efficiency is an important parameter of wireless charging.
A common form of coupling used in wireless charging is inductive coupling. A wireless charging system usually includes electromagnetically coupled transmitting and receiving coils. Energy from the primary side is transferred to the secondary side over a distance using the coil coupling. Electromagnetic induction wireless charging techniques are near field over distances comparable to a few times the diameter of the device or devices approaching one quarter of the wavelength used.
Electromagnetic induction works on the principle of a primary coil generating a predominantly magnetic field and a secondary coil being within that field so that a current is induced in the secondary coil. Coil coupling should meet the Qi specification requirements. As the distance from the primary coil is increased, more and more of the magnetic field misses the secondary coil. Even over a relatively short range, the induction method is rather inefficient, wasting much of the transmitted energy.
Common uses of inductive coupling chargers are charging the batteries of portable devices such as laptop computers, cell phones, medical implants, and electric vehicles. Resonant converters may be used in both the wireless charging pad (the transmitter circuit) and the receiver module (embedded in the load) to maximize energy transfer efficiency. This approach is suitable for universal wireless charging pads for portable electronics such as mobile phones. It has been adopted as part of the Qi wireless charging standard. It is also used for powering devices having no batteries, such as RFID patches and contactless smartcards, and to couple electrical energy from the primary inductor to the helical resonator of Tesla coil wireless power transmitters.
Inductive charging occurs when two devices—one designed to transmit power and the other to receive power—come close to one another and energy is transferred between them. The power transmitting device projects an electromagnetic field. If the receiver is placed within that electromagnetic field, power is transferred from the transmitter to the receiver. The receiver can be a power supply for any load. For example, charging pads can intelligently communicate back and forth with the devices they are charging using the electromagnetic field. In this application, the electromagnetic field used to transfer energy is modulated, allowing communication between the charging pad and the device it is charging. However, it is not always evident to the transmitting device whether there is an appropriate receiver within the electromagnetic field. Therefore, it would be useful to determine if an object were present in the electromagnetic field.
Two different types of techniques have been used to determine whether a wireless receiver to be charged is present, i.e., close enough to be wirelessly charged by the wireless transmitter, 1) digital ping techniques and 2) analog ping techniques. In digital ping techniques, the wireless transmitter attempts to communicate with the wireless receiver to determine whether or not the wireless receiver is present. Unfortunately, digital ping techniques tend to consume a significant amount of power.
In analog ping techniques, the wireless transmitter generates an electromagnetic field that is affected by the presence of the wireless receiver. The wireless transmitter determines that the wireless receiver is present by detecting the impact that the affected electromagnetic field has on its own operations. Analog ping techniques consume less power than digital ping techniques. Unfortunately, analog ping techniques are susceptible to false positive determinations when certain types of foreign objects other than the desired wireless receiver are brought near the wireless transmitter.
Conventional wireless transmitters are designed to perform both analog and digital ping techniques. These conventional wireless transmitters repeatedly perform analog pings until the wireless transmitter determines that a wireless receiver is present. The wireless transmitter then performs a digital ping to confirm whether or not the wireless receiver is actually present.